The disclosure relates to a method for roller burnishing an in particular cylindrical component part surface of a workpiece by using a roller burnishing tool comprising at least one rolling element, wherein the at least one rolling element is pressed by hydrostatic pressurization radially outwards against the component part surface and is left to roll down the component part surface by rotating the roller burnishing tool or the workpiece.
The disclosure relates further to a roller burnishing tool for roller burnishing an in particular cylindrical component part surface of a workpiece comprising a roller burnishing lance which can be inserted into the workpiece, at least one rolling element which is housed rotatably in the roller burnishing lance and which can be pressed by hydrostatic pressurization radially outwards against a bore wall of the bore, and can roll down the surface of the component part, and a rotary drive for the roller burnishing lance or the workpiece.
In the case of component parts having large high-pressure charged surfaces, such as occur by way of example in high pressure reservoirs of injectors or in pump collectors of a modular common rail system, failure of these high-pressure charged surfaces can happen as a result of high system pressure in the first instance because there are stochastically distributed inhomogeneities in the material which function as the cause of cracks, but which lie within the material tolerances. In order to prevent the formation of cracks at these places, the pressurized surface can be reformed by means of a mechanical processing so that superficial residual compressive stresses arise. In the case of cylindrical component parts or sections of component parts this can take place by way of example in that a superficial consolidation of the structure is carried out by means of ball roller burnishing, as described by way of example in DE 102009037233 B3.
Ball roller burnishing generally takes place so that the roller burnishing tool, consisting of a roller burnishing lance and several, preferably at least three, roller burnishing balls, is inserted into the cylindrical component part which is to be processed. The roller burnishing balls can be impinged with hydraulic pressure via a bore formed in the roller burnishing lance. This hydraulic pressure presses the roller burnishing balls against the cylindrical component and produces at the contact point the necessary plastic deformation of the component part. Superficial residual compressive stresses thereby arise in the component part and these have the result that any potential crack origins do not lead to the component part fracturing under system pressure (e.g. 2200 bar).
With this form of solidification by means of ball roller burnishing, particular importance is placed on the process monitoring. In particular it must be ensured that the roller burnishing balls roll down in the cylindrical component part and do not jam for example as a result of impurities or chippings in the hydraulic medium and slide along the component part. The prior art provides here that prior to processing the cylindrical surface in the component part the roller burnishing tool is inserted into a pressure measuring bush in which the radial force exerted by the roller burnishing balls as a result of the prevailing pressure of the hydraulic medium is measured. The known solution regarding the monitoring of the process does not ensure that during the entire processing of a component part the roller burnishing balls roll down in the component part. By testing the radial force in a pressure measuring bush it can only be proven that the roller burnishing balls roll down the component part before or after the actual roller burnishing process. Should a chip become jammed during the roller burnishing processing which causes a roller burnishing ball to become blocked but then this chip however becomes loose again before the end of the roller burnishing processing, the faulty processing cannot be proven by means of the pressure measuring bush so that a potential safety-critical component part results with an at least in part faulty manufacture.
The object of the present disclosure is therefore to detect a blocking of the rolling element of a roller burnishing tool. The disclosure is further aimed at proving that the rolling element has rolled down the component part throughout the entire roller burnishing process and that a blocking, even if temporarily, of the rolling element has not occurred.